Wireless radio wake-up circuits have taken attention recently due to great demand of battery powered systems. Typically, receiver wake up circuits are implemented in wireless systems as the entire system most of its time is in sleep mode consuming a very small amount of battery current. A radio wake-up circuit is basically capable of both addressing and waking up not only a more efficient but also more power and energy consuming radio front end.
Wireless sensor networks have their place in various applications like environmental monitoring applications, in which WSNs provide various information, such as temperature, air pressure, and humidity. WSNs are also used in various domains like noise monitoring, military applications, control, battlefield surveillance, home networking, etc. This area is particularly important on one hand because the energy consumption of home multi-media equipment represents an important part of the overall energy consumption. On the other hand, it is important because there is a lack of methods to optimize the energy consumption of these types of equipment. At the heart of WSNs are so-called nodes, which consist of sensors and radios (wireless receivers and transmitters). These nodes after collecting the physical information, communicate it wirelessly to the central location. The radios in these nodes are normally powered by batteries, and because they are dispersed and difficult to service, it is imperative that to extend battery life and network utility, they consume negligible power. In operation, the status of WSN nodes may be interrogated wirelessly at any time. This means that the WSN nodes need not be operating continuously “ON” and thus consuming battery power, but should only be “ON” when an interrogation event occurs. Otherwise, the node that runs out of battery power becomes disconnected from the WSN.
For wearable and hearable devices such as smart watches, bluetooth headphones, etc. wireless communication nodes are employed. In these application scenarios it may be necessary to put a collection of nodes to sleep for a long period of time. At a later time, there is a need to wake up the nodes. For achieving this purpose, an RF wake up front end circuit is designed which provides optimal performance and consumes as little energy as possible while asleep. Every time a radio is turned on, a node checks for the wakeup signal. To minimize the energy or power consumption of the system while sleeping, frequency of the radio wake up signal is minimized and checking of the wakeup signal is done by nodes whenever a radio is turned on.
A number of techniques have been adopted or implemented to decrease node or radio power consumption, which involves managing their “ON” and “OFF” time. The radio is turned periodically “ON” and “OFF”. This involves connecting the radio to a timer that periodically turns it “ON” or “OFF” according to a prescribed duty cycle. Furthermore, when RF front-ends are used for multi-mode platforms such as ZigBee or BLE, this requires a complicated firmware development for parts from different vendors (different signaling formats, protocols, burst width and repetition rate, coordination of transmit and receive signals in time domain, etc.) which makes the implementation of the interface cumbersome and increases time-to-market. Moreover number of GPIOs in existing wireless transceivers is limited and may not be enough to fulfil required operation in conjunction with external RF front end.
Prior art document U.S. Pat. No. 5,203,020 (Sato) discloses a radio telecommunication apparatus which is used in a radio telecommunication system wherein one or more base stations broadcast radio signals over a plurality of radio channels. The apparatus selects a radio channel out of the plurality of radio channels and detects the availability of the selected radio channel. In response to the unavailability of the selected radio channel, the apparatus is intermittently powered so as to detect the availability of the selected radio channel while conserving battery power consumption. Even if the availability of the selected radio channel is detected, only reception and transmission sections are intermittently powered so that the presence of information signals to be transmitted is detected. When no radio channel is available to receive radio signals from a base station, i.e., the apparatus is outside the geographic limit of the service area or radio signals from the base station are unable to reach the apparatus due to radio interference, the apparatus is intermittently powered by a battery. The duration of a power-on state is sufficient for the apparatus to detect the availability of the radio channel. Since the apparatus is intermittently powered when it is not served by a system, the battery power of the apparatus is conserved. Further, when the radio channel becomes available, the apparatus may detect its availability during the power-on state.
However, in the prior art, reducing power in radio telecommunication apparatus requires digital interface which interfaces data communication between radio unit and operation unit through firmware which is cumbersome and time-consuming.
Hence, there is a strong need and demand for eliminating multiple control lines, thus decreasing firmware development time and time-to-market for a wide range of wireless systems that employ wake up receiver schemes.